Transaxle and vehicle with it

ABSTRACT

A transaxle includes a continuously variable transmission including a speed control arm and a neutral return spring allowing a biasing force to act on the speed control arm toward a neutral position, the speed control arm configured to operate from the neutral position to a forward position or a backward position to perform a continuous speed variation. The biasing force does not act on the speed control arm when the neutral return spring ranges from the neutral position to a predetermined speed position on a forward movement side, and the biasing force acts on the speed control arm when the neutral return spring ranges from the predetermined speed position to a maximum speed position on the forward movement side.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part application based on U.S. patent application Ser. No. 14/738,410, filed on Jun. 12, 2015.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a transaxle including a hydrostatic transmission (hereinafter, “HST”), an axle driven by the HST, a transaxle connected to a control lever for operating the HST, and a vehicle including the transaxle. The invention relates particularly to the transaxle including a mechanism that automatically returns the control lever to a neutral position.

Related Art

Conventionally, as disclosed in U.S. 2015/0007555 A1, there is a well-known hydraulic transaxle that serves as each of right and left transaxles carrying respective right and left axles of a zero-turn vehicle, e.g., a lawn mower. The transaxle includes an HST, an axle and a reduction gear train transmitting power from the HST to the axle. The HST includes a hydraulic pump for receiving power from a prime mover, a hydraulic motor for outputting power to the reduction gear train, and a center section. The hydraulic pump and motor are mounted on the center section and are fluidly connected to each other via fluid passages formed in the center section. The transaxle is connected to the control lever for operating the HST, and configured to be able to switch forward and backward movements of the vehicle or perform an acceleration or deceleration operation by rotating the control lever.

The transaxle includes a mechanism that automatically returns the control lever to the neutral position by a biasing force of a neutral return spring when an operator takes off an operator's hand from the control lever after rotating the control lever from the neutral position to reach a target speed set position. The mechanism that automatically returns the control lever is useful for reducing a burden on the operator in a manipulation for reducing traveling speed of a drive wheel, and ensures safe and prompt speed reduction of the drive wheel in response to an operator's manipulation.

However, in the vehicle including the transaxle, it is necessary for the operator to continuously apply power of the operator's hand to the control lever against the force of the neutral return spring biasing the control lever toward the neutral position, when the operator wants to maintain a rotation speed of the drive wheel obtained by setting the control lever to a corresponding speed setting position. That is, in the vehicle including the transaxle, the burden on the operator increases to fatigue the operator when the operator has to endure a resistance of the control lever against the operator's manipulation force. For this reason, there is a demand for a configuration reducing the burden on the operator in the transaxle including the mechanism that returns the control lever to the neutral position.

SUMMARY OF THE INVENTION

An object of the invention is to provide a transaxle including the mechanism that returns the control lever to the neutral position and being able to reduce the burden on the operator, and a vehicle including the transaxle.

To achieve the object, a transaxle includes a continuously variable transmission including a speed control arm and a neutral return spring allowing a biasing force to act on the speed control arm toward a neutral position, the continuously variable transmission operating the speed control arm from the neutral position to a forward position or a backward position to perform a continuous speed variation. The biasing force does not act on the speed control arm when the neutral return spring ranges from the neutral position to a predetermined speed position on a forward movement side, and the biasing force acts on the speed control arm when the neutral return spring ranges from the predetermined speed position to a maximum speed position on the forward movement side.

Therefore, a dead area of the neutral return spring can be provided in the range from the neutral position to the speed position on the forward movement side. The biasing force biasing the neutral return spring toward the neutral position can be generated in the ranges from the predetermined speed position to the maximum speed position on the forward movement side. Therefore, in the case where the vehicle travels forward while being kept at a low speed, the biasing force by the neutral return spring cannot be generated in the speed control arm, and the burden on the operator can be reduced.

Preferably, in the transaxle, the biasing force acts on the neutral return spring in a whole range from the neutral position to a maximum speed position on a backward movement side.

Therefore, in the case where the vehicle travels backward, the biasing force by the neutral return spring can be generated in the speed control arm on the whole range, and the burden on the operator can be reduced.

A vehicle of the invention is a vehicle including; the transaxle in each drive wheel; and right and left control levers operated by a driver, the control lever being connected to each speed control arm.

Therefore, in the case where the vehicle travels forward while being kept at a low speed, the biasing force by the neutral return spring cannot be generated in the control lever, and the burden on the operator can be reduced. In the case where the vehicle travels backward, the biasing force by the neutral return spring is generated in the control lever through the speed control arm, and the control lever can immediately be returned to the neutral position when the operator takes off the operator's hand from the control lever, which allows the reduction of the burden on the operator.

A transaxle of the invention is a transaxle including; a transaxle casing, an axle, a hydrostatic transmission, a connecting member, a biasing member, and a pin. The axle is supported by the transaxle casing. The hydrostatic transmission is disposed in the transaxle casing, wherein the hydrostatic transmission includes a hydraulic pump and a hydraulic motor fluidly connected to each other. The hydraulic pump includes a movable swash plate having a trunnion shaft. The connecting member is disposed outside of the transaxle casing, wherein the connecting member pivotally supported on the trunnion shaft projected outward from the transaxle casing so that a rotary axis of the trunnion shaft serves as a rotary axis of the connecting member. The connecting member is linked to a control lever via a link member, wherein the control lever is configured to be rotatable between a neutral position, a first position rotated in the first direction from the neutral position, and a second position rotated from the neutral position in the second direction, the connecting member is rotated in accordance with the rotation of the control lever so that the rotational position of the trunnion shaft can be changed via the connecting member. The biasing member includes a base portion formed with a shaft hole through which the trunnion shaft can be inserted, and first arm portion and second arm portion which are elastically deformable with respect to the base portion and project outward from the base portion in mutually different phase directions in the circumferential direction of the shaft hole. The biasing member is disposed so as to be rotatable about the axis of the trunnion shaft. The pin is positioned between the first arm portion and the second arm portion of the biasing member. The pin is configured such that when the biasing member rotates in the first direction, the second arm portion can be contacted, and when the biasing member rotates in the second direction, the first arm portion can be contacted. The connecting member and the biasing member are disposed adjacent to each other in the axial direction of the trunnion shaft. The connecting member has a pressing portion projecting from the connecting member toward the biasing member, and pinched between the first arm portion and the second arm portion. When the connecting member rotates in the first direction, the pressing portion presses the first arm portion in the first direction and presses the second arm portion against the pin, and the biasing member biases the connecting member in the second direction. And when the connecting member rotates in the second direction, the pressing portion presses the second arm portion in the second direction and presses the first arm portion against the pin, and the biasing member biases the connecting member in the first direction. And when the connecting member is in the neutral position, the first arm portion of the biasing member and the pin are separated from each other, and the second arm portion of the biasing member and the pin contact each other.

Therefore, in the first direction, a dead zone of the biasing member can be provided in the rotational angle range of the connecting member from the neutral position to the predetermined angle. And in the second direction, a biasing force for biasing the connecting member to the neutral position can be generated without providing a dead zone.

Preferably, in the transaxle, the first direction is a direction in which the axle is rotated forward, and the second direction is a direction in which the axle is rotated backward.

Therefore, in the case where the vehicle travels forward while being kept at a low speed, the biasing force by the biasing member cannot be generated in the control lever, and the burden on the operator can be reduced. In the case where the vehicle travels backward, the biasing force by the biasing member is generated in the control lever through the speed control arm, and the control lever can immediately be returned to the neutral position when the operator takes off the operator's hand from the control lever, which allows the reduction of the burden on the operator.

These and other objects, features and advantages of the invention will appear more fully from the following detailed description of the invention with reference to attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of a lawn mower serving as a zero-turn vehicle equipped with right and left transaxles and right and left control levers for controlling the respective transaxles.

FIG. 2 is a plan view of the right transaxle serving as the transaxle according to the invention.

FIG. 3 is a sectional side view of the right transaxle taken along arrows of FIG. 2.

FIG. 4 is a sectional bottom view of the right transaxle taken along IV-IV arrows of FIG. 3.

FIG. 5 is a cross sectional view taken along V-V arrows of FIG. 2.

FIG. 6 is a cross sectional view taken along VI-VI arrows of FIG. 3.

FIG. 7 is a cross sectional view taken along VII-VII arrows of FIG. 3.

FIG. 8 is an enlarged view of a principal portion of FIG. 3 showing a brake.

FIG. 9 is a left side view of the right transaxle.

FIG. 10 is a right side view partly in section of the right transaxle.

FIG. 11 is a right side view of the left transaxle.

FIG. 12 is a right side view of a speed control arm of the right transaxle located at a neutral position.

FIG. 13 is a right side view of the speed control arm rotated from the neutral position in the direction for forward rotation of the corresponding axle when the speed control arm reaches a predetermined angle.

FIG. 14 is a right side view of the speed control arm rotated in the direction for forward rotation of the corresponding axle when the speed control arm reaches a maximum angle.

FIG. 15 is a right side view of the speed control arm rotated in the direction for backward rotation of the corresponding axle when the speed control arm reaches a maximum angle.

FIG. 16 is a graph showing the relationship between the operator's manipulation force required to operate the speed control arm in the direction for forward and backward rotation against force of neutral return spring and the motor rotation speed.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a lawn mower (hereinafter simply referred to as “vehicle”) 100 serving as a typical zero-turn vehicle is equipped with right and left transaxle 1R and 1L carrying respective right and left axles 2R and 2L, and is equipped with right and left control levers 60R and 60L for controlling respective right and left transaxles 1R and 1L. Hereinafter, all the descriptions will be given on an assumption that right and left transaxles 1R and 1L are provided therebetween with a centerline disposed at the lateral middle position of vehicle 100 and extended in the fore-and-aft direction of vehicle 100, so that the side or direction of each of transaxles 1R and 1L close to the centerline is referred to as “proximal”, and the side or direction of each of transaxles 1R and 1L opposite or away from the centerline is referred to as “distal”. Therefore, right transaxle 1R has its left side as its proximal side, and has its right side as its distal side, and left transaxle 1L has its right side as its proximal side, and has its left side as its distal side.

Vehicle 100 includes a vehicle body frame 4 having right and left parallel sideboards 4 a extended in the fore-and-aft horizontal direction thereof. Vehicle body frame 4 supports right and left transaxles 1R and 1L so that transaxle casings 10 of right and left transaxles 1R and 1L are disposed in the inside of vehicle body frame 4, i.e., between right and left sideboards 4 a when viewed in plan. Right axle 2R is extended rightward from transaxle casing 10 of right transaxle 1R to the outside of right sideboard 4 a of vehicle body frame 4 so as to be fixed at a distal end thereof to right drive wheel 3R. Left axle 2L is extended leftward from transaxle casing 10 of left transaxle 1L to the outside of left sideboard 4 a of vehicle body frame 4 so as to be fixed at a distal end thereof to left drive wheel 3L. Right and left transaxles 1R and 1L are disposed in vehicle 100 so as to laterally extend right and left axles 2R and 2L coaxially to each other.

Right and left drive wheels 3R and 3L serving as rear wheels of vehicle 100 are disposed on the right and left outsides of a rear portion of vehicle body frame 4. A front end portion of vehicle body frame 4 supports castors (or front wheels) 5 serving as front wheels (or a front wheel) of vehicle 100. A mower unit 6 is disposed below a fore-and-aft middle portion of vehicle body frame 4 between front wheels 5 and rear wheels 3R and 3L. Mower unit 6 is provided with PTO (Power Take Off) pulleys 9.

Further, vehicle 100 is equipped with an unshown prime mover, e.g., an engine, whose output power is transmitted from a double drive pulley 90 of the prime mover via a belt 7 to input pulleys 14 of respective right and left transaxles 1R and 1L. Belt 7 is looped over one pulley part of double drive pulley 90 and right and left input pulleys 14, and a tension pulley 91 applies a required tension onto belt 7.

Another belt 8 is looped over the other pulley part of double drive pulley 90 and PTO pulleys 9. Belt 8 is provided with a tension clutch pulley 92 adjacent to the proximal left side surface of right transaxle 1R. When pulley 92 is pressed against belt 8 as drawn in solid lines in FIG. 1, pulley 92 applies a tension to belt 8 so that the rotary power of drive pulley 90 is transmitted to PTO pulleys 9 via belt 8 so as to drive rotary blades of mower unit 6. When pulley 92 is rotated away from belt 8 and toward right transaxle 1R as phantom lines in FIG. 1, the tension clutch serving as pulley 92 is clutched off, so that belt 8 has no tension, whereby PTO pulleys 9 do not receive the rotary power of drive pulley 90 for driving the rotary blades of mower unit 6.

Transaxle casings 10 of right and left transaxles 1R and 1L incorporate respective parking brakes 69. Therefore, to operate parking brakes 69 of right and left transaxles 1R and 1L, vehicle 100 is provided with a parking brake control mechanism 169 that includes a parking brake pedal 64 serving as a manipulator for simultaneously shifting both parking brakes 69 of right and left transaxles 1R and 1L between an activation state and an inactivation state. Alternatively, the manipulator may be a lever or the like. Parking brake pedal 64 is located in vehicle 100 available for depression of parking brake pedal 64 by an operator's foot. By depressing parking brake pedal 64, both right and left drive wheels 3R and 3L are braked.

Brake control mechanism 169 includes right and left link rods 19R and 19L extended rearward from parking brake pedal 64 to respective transaxle casings 10 of right and left transaxles 1R and 1L. When viewed in plan, right and left link rods 19R and 19L are extended in the fore-and-aft direction of vehicle 100 in the space between right and left sideboards 4 a and between transaxle casings 10 of right and left transaxles 1R and 1L, i.e., on the respective proximal sides of transaxle casings 10 of right and left transaxles 1R and 1L. Incidentally, each of right and left transaxles 1R and 1L is configured so that one of right and left sides, i.e., proximal and distal sides, of transaxle casing 10 is selective to have each link rod 19R or 19L. In other words, in the embodiment shown in FIG. 1, the proximal sides of transaxle casings 10 of right and left transaxles 1R and 1L are selected for arrangement of right and left link rods 19R and 19L.

Right and left link rods 18 are extended along respective right and left sideboards 4 a rearward from respective right and left control levers 60R and 60L to respective speed control arms 46 provided on distal sides of respective transaxle casings 10 of right and left transaxles 1R and 1L. When viewed in plan, right and left link rods 18 are extended in the fore-and-aft direction of vehicle 100 along respective right and left sideboards 4 a. Incidentally, each of right and left transaxles 1R and 1L is configured so that one of right and left sides, i.e., proximal and distal sides, of transaxle casing 10 is selective to have speed control arm 46. In other words, in the embodiment shown in FIG. 1, the distal sides of transaxle casings 10 of right and left transaxles 1R and 1L are selected for arrangement of speed control arms 46 and right and left link rods 18. Further, as understood from FIG. 2 illustrating representative right transaxle 1R, each of right and left transaxles 1R and 1L includes a neutral returning spring 47 on the distal side of transaxle casing 10 with speed control arm 46.

As understood from FIG. 3 illustrating representative right transaxle 1R, right control lever 60R is operable to change the tilt angle and direction of a later-discussed movable swash plate 44 of an HST 20 of right transaxle 1R so as to change the rotary speed and direction of right rear wheel 3R. Left control lever 60L is operable to change the tilt angle and direction of movable swash plate 44 of HST 20 of left transaxle 1L so as to change the rotary speed and direction of left rear wheel 3L. When right and left control levers 60R and 60L are synchronously manipulated by an operator, movable swash plates 44 of HSTs 20 of right and left transaxles 1R and 1L are synchronously controlled to change the straight travel speed of vehicle 100 in either the forward direction or the backward direction. When right and left control levers 60R and 60L are independently manipulated, movable swash plates 44 of HSTs 20 of right and left transaxles 1R and 1L are differentially controlled so as to control the turn direction, angle, and speed of vehicle 100.

Referring to FIGS. 3 to 10, representative right transaxle 1R will be described on an assumption that right and left transaxles 1R and 1L are symmetric with respect to the above-mentioned laterally middle fore-and-aft centerline drawn in vehicle 100 shown in FIG. 1. Therefore, detailed description of left transaxle 1L is omitted because it is identical or similar to right transaxle 1R, excluding a later-discussed difference of connection of left link rod 19L to left transaxle 1L from connection of right link rod 19R to right transaxle 1R.

Referring to FIG. 3, right transaxle 1 includes transaxle casing 10, HST 20 disposed in a front portion of transaxle casing 10, a right axle 2R journalled by a rear portion of transaxle casing 10, and a reduction gear train 70 disposed in the rear portion of transaxle casing 10 so as to drivingly connect HST 20 to right axle 2R.

Transaxle casing 10 includes an upper housing 11, a lower housing 12, and a top cover 13. Bolts 16 are screwed upward to fasten a flanged top edge of lower housing 12 to a bottom edge of upper housing 11 fringing a bottom opening of upper housing 11. Bolts 17 are screwed downward to fasten a flanged bottom edge of top cover 13 to a top edge of a rear half portion of upper housing 11 fringing a top opening of the rear half portion of upper housing 11. By joining upper housing 11 and lower housing 12 to each other at respective horizontal joint surfaces 11 k and 12 e thereof, a cavity of transaxle casing 10 is formed, and upper and lower housings 11 and 12 form a partition wall 10 c that divides the cavity of transaxle casing 10 into a front HST chamber 10 a and a rear gear chamber 10 b.

The rear portion of upper housing 11 defining gear chamber 10 b accommodates reduction gear train 70. Top cover 13 covers an upper portion of reduction gear train 70 in gear chamber 10 b. The front portions of upper and lower housings 11 and 12 defining front HST chamber 10 a accommodate HST 20.

HST 20 includes a center section 30, a hydraulic pump 40, and a hydraulic motor 50. Center section 30 is entirely formed by casting integrally with a horizontal pump port block portion 31, a slant motor port block portion 32, a bypass valve block portion 33, and a plurality (in this embodiment, four) of bolt boss portions 34 and 35. Motor port block portion 32 is joined to pump port block portion 31 so as to extend rearwardly upward from a rear end of pump port block portion 31. Bypass valve block portion 33 projects downward from motor port block portion 32 so as to extend in the lateral horizontal portion.

As shown in FIG. 5, pump port block portion 31 is formed therein with right and left pump kidney ports 31 b and 31 c and a pump shaft hole 31 d between pump kidney ports 31 b and 31 c. A horizontal pump mounting surface 31 a is formed on a top end of pump port block portion 31. Pump kidney ports 31 b and 31 c and pump shaft hole 31 d are extended vertically upward so as to be open at horizontal pump mounting surface 31 a.

A horizontal filter mounting surface 31 e is formed on a bottom end of pump port block portion 31. A circumferential area of filter mounting surface 31 e is provided to contact a top edge of a cylindrical filter 26. In this regard, when HST 20 is disposed in transaxle casing 10, filter 26 contacting filter mounting surface 31 e of center section 30 is submerged in a fluid sump in chamber 10 a so that fluid is filtered by filter 26 when the fluid penetrates filter 26 from the fluid sump in chamber 10 a to the inside space of filter 26.

Right and left main fluid passages 36 and 37 are formed in pump port block portion 31 so as to extend in the horizontal fore-and-aft direction. Referring to FIG. 3, right and left charge check valves 21 are disposed in respective front portions of right and left main fluid passages 36 and 37. Right and left suction ports 31 f are open at the bottom surface of center section 30 surrounded by filter mounting surface 31 e. The fluid inside of filter 26 is introduced into either hydraulically depressed main fluid passage 36 or 37 via suction port 31 f and corresponding charge check valve 21, thereby being supplied as supplementary hydraulic fluid to the closed fluid circuit of HST 20.

Referring to FIG. 4, motor port block portion 32 is formed therein with right and left motor kidney ports 32 b and 32 c and a motor shaft hole 32 d between motor kidney ports 32 b and 32 c. A slant upper end of motor port block portion 32 is formed as a rearwardly downward slant motor mounting surface 32 a. Right and left main fluid passages 36 and 37 are extended rearward into motor port block portion 32 so as to be joined at rear ends thereof to respective right and left motor kidney ports 32 b and 32 c.

Referring to FIG. 5, hydraulic pump 40 includes a pump shaft 41, a pump cylinder block 42, plungers 43, and a movable swash plate 44. Pump shaft 41 is fittingly passed through pump shaft hole 31 d in pump port block portion 31 of center section 30 rotatably relative to center section 30. Pump cylinder block 42 is formed with a center through hole serving as a pump shaft hole 42 a and with cylinder bores 42 b aligned radially around pump shaft hole 42 a. Pump shaft 41 is fittingly passed through pump shaft hole 42 a unrotatably relative to pump cylinder block 42. Pump cylinder block 42 is slidably rotatably fitted onto pump mounting surface 31 a so as to fluidly connect cylinder bores 42 b therein to pump kidney ports 31 b and 31 c. Plungers 43 are fitted into respective cylinder bores 42 b reciprocally in the axial direction of pump shaft 41. Movable swash plate 44 has a bearing 44 a abutting against heads of plungers 43 projecting from pump cylinder block 42. In this way, hydraulic pump 40 is configured as an axial piston type hydraulic pump.

A front top portion of the ceiling wall of transaxle housing 11 is formed as a pump shaft support portion 11 b for supporting pump shaft 41. Upper housing 11 is formed through right and left side walls of pump support portion 11 b with right and left symmetric trunnion holes 11 c. Movable swash plate 44 of hydraulic pump 40 is a trunnion type movable swash plate, which is formed with right and left symmetric feet 44 b having respective right and left symmetric trunnion holes 44 c. Right and left fixture pins 45 a fasten right and left feet 44 b of movable swash plate 44 to right and left trunnion shafts 45 fitted in trunnion holes 44 c.

Pump shaft support portion 11 b is formed with a vertical through hole bh. An upper portion of pump shaft 41 projecting upward from pump cylinder block 42 fitted on pump mounting surface 31 a of center section 30 is freely passed through movable swash plate 44 and through vertical through hole bh of pump shaft support portion 11 b so as to project upward from pump shaft support portion 11 b of transaxle housing 11. A bearing 41 a and a fluid seal 41 b are fitted in through hole bh of pump shaft support portion 11 b so as to be interposed between pump shaft 41 and pump shaft support portion 11 b of transaxle housing 11. Input pulley 14 and a cooling fan 15 are fixed on the upper portion of pump shaft 41 projecting upward from pump support portion 11 b of transaxle housing 11.

Referring to FIG. 6, hydraulic motor 50 includes a motor shaft 51, a motor cylinder block 52, plungers 53, and a movable swash plate 54. Motor shaft 51 is fitted into motor shaft hole 32 d in motor port block portion 32 of center section 30 rotatably relative to center section 30. Motor cylinder block 52 is formed with a center through hole serving as a motor shaft hole 52 a and with cylinder bores 52 b aligned radially around motor shaft hole 52 a. Motor shaft 51 is fittingly passed through motor shaft hole 52 a unrotatably relative to motor cylinder block 52. Motor cylinder block 52 is slidably rotatably fitted onto motor mounting surface 32 a of center section 30 so as to fluidly connect cylinder bores 52 b therein to motor kidney ports 32 b and 32 c. Cylinder bores 52 b are fluidly connected to cylinder bores 42 b in pump cylinder block 42 via main fluid passages 36 and 37 of the closed fluid circuit of HST 20 (see FIG. 5).

Plungers 53 are fitted into respective cylinder bores 52 b reciprocally in the axial direction of motor shaft 51. A bearing abuts against heads of plungers 53 projecting from motor cylinder block 52 so as to serve as movable swash plate 54. In this way, hydraulic motor 50 is configured as an axial piston type hydraulic motor.

Referring to FIG. 3, a motor support member 56 is disposed in gear chamber 10 b, and is fastened to upper housing 11 by bolts 57. Movable swash plate 54 is a cradle type movable swash plate, which is rotatably and slidably fitted to motor support member 56, and abuts against heads of plungers 53 projecting from motor cylinder block 52. Referring to FIG. 6, upper housing 11 is formed through right and left side walls of a fore-and-aft intermediate portion thereof with right and left symmetric trunnion holes 11 h. Movable swash plate 54 is fixed at either a right or left end thereof to a trunnion arm 55. A trunnion shaft 55 a projects horizontally from trunnion arm 55 and is fitted into one of right and left trunnion holes 11 h rotatably relative to upper housing 11. Remaining trunnion hole 11 h is plugged by a cap 65.

An operation lever (not shown) is fixed on a tip portion of trunnion shaft 55 a projecting outward from transaxle casing 10. This operation lever for controlling movable swash plate 54 of hydraulic motor 50 can be used to adjust an output scale of transaxle 1R or 1L in correspondence to a vehicle maker's demand, or to minutely adjust the output performance of right and left transaxles 1R and 1L for keeping the ability of vehicle 100 in straight traveling when control levers 60R and 60L are operated for the straight traveling. In which direction trunnion shaft 45 projects is selected in consideration of facility in work for the above-mentioned output adjustment of transaxle 1R or 1L.

Right and left trunnion shafts 45 have respective tip portions projecting outward from the right and left side surfaces, i.e., distal and proximal side surfaces, of upper housing 11 of transaxle casing 10. Referring to FIG. 4, a speed control arm 46 is fixed on the right tip portion of right trunnion shaft 45 projecting outward from the distal right side surface of upper housing 11 so that the tilt angle and direction of movable swash plate 44 of hydraulic pump 40 is controlled by rotating speed control arm 46.

Neutral return spring 47 is wound around the tip portion of right trunnion shaft 45 between speed control arm 46 and the distal right side surface of upper housing 11 so as to have both end portions Eu and El twisted to cross each other and extended rearward. A nut 46 a is screwed on the tip portion of right trunnion shaft 45 outside of speed control arm 46 so as to prevent speed control arm 46 and neutral return spring 47 from falling from right trunnion shaft 45.

Referring to FIG. 10, speed control arm 46 has a basal end portion attached on the right tip portion of right trunnion shaft 45, and has a tip portion formed with a later-discussed hole 46 c into which a rear end portion of a later-discussed link rod 18 is fitted, so that speed control arm 46 is extended upward from the basal end thereof to the tip end thereof. Speed control arm 46 is formed with a rear branching portion that extends rearward from the basal end portion of speed control arm 46 so as to cover front halves of end portions Eu and El of neutral return spring 47 extended rearward from their mutual crossing portions. The rear branching portion is bent to have a rear end portion that is extended proximally toward the distal right side surface of upper housing 11 of transaxle casing 10 so as to serve as a pressure plate 46 b. Of both end portions Eu and El of neutral return spring 47, a rear half of upper end portion Eu is extended to above pressure plate 46 b, a rear half of lower end portion El is extended to below pressure plate 46 b, and pressure plate 46 b is disposed in halfways of rear-extended-shaped end portions Eu and El of neutral return spring 47. When speed control arm 46 is disposed at the neutral position, upper end portion Eu of neutral return spring 47 is not in contact with an eccentric pin 49 (to be described later), but lower end portion El is in contact with eccentric pin 49.

When pressure plate 46 b moves upward by rotating speed control arm 46, pressure plate 46 b pushes upper end portion Eu of neutral return spring 47 upward. As upper end portion Eu of neutral return spring 47 pushed by pressure plate 46 b moves upward after lower end portion El of neutral return spring 47 abuts against an eccentric pin 49, the gap between upper and lower end portions Eu and El of neutral return spring 47 is expanded so that neutral return spring 47 generates a biasing force that biases upper and lower end portions Eu and El toward each other.

The right side wall of upper housing 11 of transaxle casing 10 adjacently rearward from right trunnion shaft 45 having speed control arm 46 and neutral returning spring 47 thereon is formed with an eccentric pin hole 11 d, and a laterally horizontal axis shaft 49 a of eccentric pin 49 is fitted into eccentric pin hole 11 d. In this regard, the right and left side walls of transaxle housing 11 adjacently rearward from right and left trunnion holes 11 c are formed to have sufficient thickness before boring eccentric pin hole 11 d so that either the right or left wall can be selectively bored with eccentric pin hole 11 d.

Eccentric pin 49 is fitted on a portion of axis shaft 49 a projecting outward from transaxle housing 11 and a nut is screwed on a distal end of axis shaft 49 a so as to fasten eccentric pin 49 to axis shaft 49 a. The nut is loosened to abut lower end portions El of neutral return spring 47 on eccentric pin 49 as illustrated in FIG. 12, and the nut is tightened when the rotation of eccentric pin 49 is adjusted to reach the real neutral position of movable swash plate 44 for stopping the oil discharged from hydraulic pump 40, which allows eccentric pin 49 to be fixed. In this regard, by loosening the nut, the rotational position of eccentric pin 49 pinched by neutral returning spring 47 relative to axis shaft 49 a can be changed to adjust the neutral position of speed control arm 46 relative to the neutral position of movable swash plate 44.

Reduction gear train 70 disposed in gear chamber 10 b will now be described.

Referring to FIG. 6, a laterally horizontal intermediate gear shaft 72 is disposed in gear chamber 10 b. Upper housing 11 is formed with right and left support portions 11 i that journal right and left ends of intermediate gear shaft 72. A bevel gear 73 is formed with a spur pinion 74, and is fixed on intermediate gear shaft 72. Bevel gear 73 meshes with a bevel pinion 71 fixed on an upper portion of motor shaft 51.

Referring to FIG. 4, a spur bull gear 77 is fixed on right axle 2R supported by upper housing 11 and meshes with spur pinion 74. Therefore, bevel pinion 71, bevel gear 73, spur pinion 74 and spur bull gear 77 constitute reduction gear train 70 for transmitting power from motor shaft 51 of HST 20 to right axle 2R.

Referring to FIG. 7, intermediate gear shaft 72 is pivotally supported by upper housing 11 via right and left bearings 72 a and 72 b fixed in respective right and left support portions 11 i of upper housing 11 so as to be rotatable relative to transaxle casing 10. Referring to FIG. 10, bearing covers 75 are fastened to respective support portions 11 i of upper housing 11 by bolts 76 so as to cover top portions of respective bearings 72 a and 72 b.

Referring to FIG. 4, a discoid magnet 66 is disposed in gear chamber 10 b below a later-discussed brake operation shaft 79, and is supported by upper and lower housings 11 and 12 joined to each other so as to adsorb iron powder mixed in fluid in gear chamber 10 b.

A defoaming pipe 61 is extended in the fore-and-aft horizontal direction, and is interposed between an upper portion of the front portion of upper housing 11 defining HST chamber 10 a and a front portion of top cover 13 defining gear chamber 10 b. A front end portion of defoaming pipe 61 is bent to extend vertically downward, and is fitted into a vertical hole of a boss 11 f formed at a rear portion of pump shaft support portion 11 b of upper housing 11, so that a downwardly open front end of defoaming pipe 61 is open to the upper portion of HST chamber 10 a. A rear end portion of defoaming pipe 61 is fitted into a fore-and-aft horizontal hole of a boss 13 b formed at a front portion of top cover 13, so that a rearwardly open rear end of defoaming pipe 61 is open to the upper portion of gear chamber 10 b. Therefore, air foam rising in the fluid in HST chamber 10 a is introduced into defoaming pipe 61 and is moved from HST chamber 10 a to gear chamber 10 b via defoaming pipe 61.

A top portion of top cover 13 is provided with a breather 62 for breathing an air space in gear chamber 10 b to the atmosphere. In the upper portion of gear chamber 10 b in top cover 13, a horizontal partition plate 63 is settled just below breather 62 so as to prevent fluid splashed up by the gears of reduction gear train 70 from entering breather 62. A metal plate serves as partition plate 63, for example. Partition plate 63 is formed with notches 63 a at front and rear edges, and ribs 13 c formed on top cover 13 to define passages for air and fluid between gear chamber 10 b and breather 62 are fittingly passed through front and rear notches 63 a of partition plate 63.

A parking brake 69 of right transaxle 1R will now be described.

Referring to FIG. 8, motor support member 56 is formed with a rearwardly upward slant through hole 56 a. A bearing 51 a is fitted in hole 56 a. The upper portion of motor shaft 51 projecting rearwardly upward from motor cylinder block 52 is passed through movable swash plate 54 and is journalled by motor support member 56 via bearing 51 a.

Motor support member 56 is formed with a flat surface 56 b perpendicular to motor shaft 51. Bevel pinion 71 is fixed on the tip portion of motor shaft 51. More specifically, bevel pinion 71 is spline-fitted on the tip portion of motor shaft 51, and a circular clip 51 b is engaged on the tip portion of motor shaft 51 so as to locate bevel pinion 71.

An annular brake surface member 59 a is fitted on flat surface 56 b of motor support member 56, and is partly extended onto an upper surface of motor support member 56. Brake discs 58 are disposed parallel to brake surface member 59 a, and are engaged with teeth of bevel pinion 71 so as to be unrotatable relative to bevel pinion 71 and so as to be slidable on bevel pinion 71 in the axial direction of motor shaft 51. Plate-shaped retainers 59 b as many as brake discs 58 are layered alternately with brake discs 58, and are fixed to the upper surface of motor support member 56. Retainers 59 b are bent to extend parallel to brake discs 58 so as to be layered alternately with brake discs 58, thereby restricting the slidable range of brake discs 58. Outermost retainer 59 b prevents brake discs 58 from moving to disengage from bevel pinion 71.

Referring to FIG. 7, right and left symmetric shaft holes 11 j are formed through right and left side walls of upper housing 11, and laterally horizontal brake operation shaft 79 is pivotally supported at right and left end portions thereof through right and left shaft holes 11 j rotatably relative to upper housing 11. The left end of brake operation shaft 79 projecting outward from upper housing 11 is selected to have a parking brake arm 78 fixed thereon. More specifically, brake operation shaft 79 has the end portion projecting outward from the proximal side surface of transaxle casing 10 opposite the distal side surface of transaxle casing 10 from which right axle 2R projects outward. Parking brake arm 78 is disposed in the proximal outside of transaxle casing 10 and is connected to the projecting end portion of brake operation shaft 79 pivotally on the axis of brake operation shaft 79.

Referring to FIG. 3, in gear chamber 10 b, when viewed in side, a triangular space is provided between rearwardly upward extended hydraulic motor 50 and bull gear 77, and is used to locate brake operation shaft 79 and a pressure arm 80. In gear chamber 10 b, pressure arm 80 is fixed on brake operation shaft 79. A tip portion of pressure arm 80 is formed with a pawl 80 a to be pressed against brake discs 58. When parking brake arm 78 is located at an unbraking position, pawl 80 a is separated from brake discs 58. When parking brake arm 78 is located at a braking position, as shown in FIG. 8, pawl 80 a is pressed against brake discs 58 so as to press brake discs 58 against surfaces of retainers 59 b and brake surface member 59 a, thereby braking bevel pinion 71 together with brake discs 58.

Referring to FIG. 1, as mentioned above, vehicle 100 is provided with parking brake control mechanism 169 configured to rotate parking brake arms 78 of right and left transaxles 1R and 1L according to operation of parking brake pedal 64. Parking brake control mechanism 169 will now be described in detail. As shown in FIG. 1, each of right and left link rods 19R and 19L has a front end serving as a starting end 19 a, and has a rear end serving as a terminal end 19 b. Starting ends 19 a of right and left link rods 19R and 19L are connected to parking brake pedal 64.

Referring to FIG. 1, while right and left axles 2R and 2L of respective right and left transaxles 1R and 1L are disposed coaxially to each other, terminal ends 19 b of respective link rods 19R and 19L are located at different positions in the fore-and-aft direction of vehicle 100 so as to be connected to respective right and left transaxles 1R and 1L. More specifically, terminal end 19 b of right link rod 19R is disposed forward from terminal end 19 b of left link rod 19L.

Now, left transaxle 1L having parking brake arm 78 connected to left link rod 19L will be described with reference to FIG. 11. Left transaxle 1L includes parking brake arm 78 fixed on the right end portion of brake operation shaft 79 projecting rightward from the proximal right side surface of transaxle casing 10. In this regard, parking brake arm 78 is formed in a basal end portion thereof with a pivot hole 78 a, into which the proximal right end portion of brake operation shaft 79 is inserted fixedly (i.e., unrotatably relative to parking brake arm 78). Parking brake arm 78 of left transaxle 1L is extended upward from its basal end portion provided on the right end portion of brake operation shaft 79 so as to have an upper end portion formed with a connection hole 78 b, into which terminal end 19 b of left link rod 19L is fitted pivotally (i.e., rotatably relative to parking brake arm 78).

In this regard, as mentioned above, tension pulley 91 is disposed at the proximal right side of the proximal right side surface of transaxle casing 10 of left transaxle 1L adjacently to left transaxle 1L, however, it cannot happen that tension pulley 91 approaches transaxle casing 10 of left transaxle 1L so as to interfere with left link rod 19L, because tension pulley 91 that is fixed in location except for its rotatability according to driving belt 7 does not come to intersect left link rod 19L. Therefore, left transaxle 1L employs the ordinary way for its connection to left link rod 19L so that terminal end 19 b of left link rod 19L is connected to the upper end portion of parking brake arm 78 extended upward from its basal end portion fixed on the end of brake operation shaft 79.

When parking brake pedal 64 is depressed, left link rod 19L is pulled together with right link rod 19R forward so as to rotate the upper end portion of parking brake arm 78 of left transaxle 1L forward, thereby causing brake operation shaft 79 to rotate clockwise as designated by an arrow B1 when the proximal right side surface of transaxle casing 10 of left transaxle 1L is viewed as shown in FIG. 11, i.e., counterclockwise in the left side view of left transaxle 1L. This rotation of brake operation shaft 79 causes pressure arm 80 to rotate so as to press pawl 80 a against brake discs 58, thereby braking left axle 2L of left transaxle 1L.

On the contrary, right transaxle 1R having parking brake arm 78 connected to right link rod 19R via a relay arm 81 and a link rod 83 will be described. As mentioned above, vehicle 100 includes tension clutch pulley 92 disposed adjacently at the proximal left side of transaxle casing 10 of right transaxle 1R. When pulley 92 is operated for disengaging the tension clutch, pulley 92 approaches the proximal left side surface of transaxle casing 10 of right transaxle 1R. In this state, if right link rod 19R were operatively connected to right transaxle 1R in the same way as the connection of left link rod 19L to left transaxle 1L, i.e., if parking brake arm 78 of right transaxle 1R were extended upward from brake operation shaft 79, and right link rod 19R were directly connected at terminal end 19 b thereof to the upper end portion of parking brake arm 78, link rod 19R would interfere with pulley 92 operated for disengaging the tension clutch.

To avoid the interference of tension clutch pulley 92 with a link rod connected to parking brake arm 78, first, parking brake arm 78 of right transaxle 1R is extended downward from brake operation shaft 79 so as to have a link rod connected to a lower end portion thereof via connection hole 78 b below pulley 92. More specifically, parking brake arm 78 of right transaxle 1R is identical to above-mentioned parking brake arm 78 of left transaxle 1L. The proximal left end portion of brake operation shaft 79 projecting from the proximal left side surface of transaxle casing 10 of right transaxle 1R is fixedly inserted into pivot hole 78 a in the basal end portion of parking brake arm 78 of right transaxle 1R. Parking brake arm 78 of right transaxle 1R is extended downward from the basal end portion thereof provided on the left end portion brake operation shaft 79 so as to have connection hole 78 b in its lower end portion.

Therefore, in each of transaxles 1R and 1L, parking brake arm 78 is unrotatable relative to brake operation shaft 79 and is rotatable relative to transaxle casing 10. Referring to FIGS. 4, 9 and 11, parking brake arm 78 has a pivotal axis P5 coinciding to the axis of brake operation shaft 79, and parking brake arm 78 is interlocked with brake operation shaft 79 so that rotation of parking brake arm 78 causes rotation of brake operation shaft 79. Incidentally, parking brake arm 78 may not be completely fixed to brake operation shaft 79, i.e., parking brake arm 78 may have a play range for rotation relative to brake operation shaft 79, only if pivotal axis P5 of parking brake arm 78 coinciding to the axis of brake operation shaft 79 is ensured and the rotation of parking brake arm 78 out of the rotational play range causes rotation of brake operation shaft 79.

For the above-mentioned purpose of preventing brake arm 78 or a link rod connected to brake arm 78 from interfering with other members in vehicle 100, it may be conceivable that parking brake arm 78 is extended downward and right link rod 19R is directly connected to the lower end portion of parking brake arm 78 of right transaxle 1R. However, it causes another problem that the rotational direction of brake operation shaft 79 according to depression of parking brake pedal 64 comes opposite its proper rotational direction for applying the parking brake. In this regard, as understood from the description about rotation of brake operation shaft 79 of left transaxle 1L, the proper rotational direction of brake operation shaft 79 for activating parking brake 69 for braking motor shaft 51 is counterclockwise in the left side view of each transaxle 1R or 1L. On the contrary, since link rod 19R is pulled forward together with link rod 19L according to the depression of parking brake pedal 64, brake operation shaft 79 would rotate clockwise in the left side view of right transaxle 1R, i.e., opposite the proper direction for applying the parking brake, according to the forward movement of right link rod 19R by depressing parking brake pedal 64, if terminal end 19 b of link rod 19R were directly connected to the lower end portion of parking brake arm 78 extended downward from brake operation shaft 79.

Therefore, to match the rotational direction of brake operation shaft 79 according to depression of parking brake pedal 64 with its proper rotational direction for applying the parking brake, parking brake control mechanism 169 includes relay arm 81 and link rod 83 interposed between right link rod 19R and the lower end portion of downwardly extended parking brake arm 78 of right transaxle 1R, as shown in FIGS. 1, 2, 4, 7, 9 and 10. Incidentally, it should be noticed that link rod 83 is omitted in FIG. 1 just for convenience in illustration.

Relay arm 81 is extended substantially vertically, and is pivoted at the vertical intermediate portion thereof on a pivotal axis provided on the proximal left side of transaxle casing 10 of right transaxle 1R so as to have upper and lower ends opposite each other with respect to the pivotal axis of relay arm 81. Relay arm 81 includes an upper arm portion 81 a extended upward from the pivotal axis to the upper end of relay arm 81 so as to have an upper end portion connected to link rod 19R. Relay arm 81 includes a lower arm portion 81 b extended downward from the pivotal axis to the lower end of relay arm 81 so as to have a lower end portion connected to link rod 83, so that link rod 83 is interposed between the lower end portion of relay arm 81 and the lower end portion of parking brake arm 78 of right transaxle 1R, so that link rod 83 is disposed below tension clutch pulley 92 safely from interfering with pulley 92. Relay arm 81 functions to convert the forward movement (as designated by an arrow B0 in FIG. 9) of right link rod 19R connected at its terminal end 19 b to the upper end portion of relay arm 81 according to depression of parking brake pedal 64 into the rearward movement of link rod 83 interposed between the lower end portion of relay arm 81 and the lower end portion of parking brake arm 78. As a result, when parking brake pedal 64 is depressed, link rod 83 connected at its terminal end 83 b to the lower end portion of parking brake arm 78 is moved rearward so as to rotate brake operation shaft 79 counterclockwise in the left side view (as designated by arrow B1 in FIG. 9), i.e., in the proper rotational direction to apply parking brake 69 of right transaxle 1R.

As mentioned above, link rod 83 is disposed below pulley 92 to avoid its interference with pulley 92. On the other hand, to prevent relay arm 81 from interfering with tension clutch pulley 92, relay arm 81 may be disposed at any position on the proximal left side of transaxle casing 10 of right transaxle 1R forward from pulley 92. For example, a lateral horizontal pivot shaft other than trunnion shafts 45 of movable swash plate 44 may be supported at a front end portion of transaxle casing 10 so as to have relay arm 81 pivoted thereon, or relay arm 81 may be pivoted on a projection formed on transaxle casing 10 (e.g., upper housing 11). However, in this embodiment, left trunnion shaft 45 serves as a relay shaft for pivoting relay arm 81 thereon in consideration of the convenience of the left end portion of left trunnion shaft 45, which is left without speed control arm 46 thereon, and which is disposed forward from pulley 92 appropriately to avoid interference with pulley 92.

In this regard, relay arm 81 is provided on the left end portion of left trunnion shaft 45 projecting leftwardly outward from the proximal left side surface of upper housing 11, while speed control arm 46 is provided on the right end portion of right trunnion shaft 45 projecting rightwardly outward from the distal right side surface of upper housing 11. Relay arm 81 is formed in the intermediate portion thereof with a pivot hole 81 c. The left end portion of left trunnion shaft 45 is passed through pivot hole 81 c. Relay arm 81 provided on left trunnion shaft 45 is formed with an upper connection hole 81 d in the upper portion of upper arm portion 81 a extended upward from pivot hole 81 c, and is formed with a lower connection hole 81 e in the lower end portion of lower arm portion 81 b extended downward from pivot hole 81 c. A circular clip 82 is engaged on the left end portion of left trunnion shaft 45 at the proximal outside of relay arm 81 so as to prevent relay arm 81 falling from left trunnion shaft 45, however, so as to allow relay arm 81 to rotate relative to trunnion shafts 45 of movable swash plate 44. In other words, relay arm 81 has a pivotal axis P1 coinciding to the axis of trunnion shaft 45, i.e., the axis of trunnion shaft 45 serves as pivotal axis P1 for relay arm 81, however, relay arm 81 is not fixed to trunnion shaft 45, so that rotation of relay arm 81 does not cause rotation of trunnion shafts 45.

Referring to FIG. 2, terminal end 19 b of right link rod 19R is bent distally, i.e., rightward, toward transaxle casing 10 and is fitted into connection hole 81 d in the upper end portion of relay arm 81. Terminal end 19 b of link rod 19R has a pivotal axis P2 coinciding to a central axis of connection hole 81 d. In other words, terminal end 19 b of link rod 19R and the upper end portion of relay arm 81 are connected to each other so that they are centered on pivotal axis P2 rotatably relative to each other. In this regard, right link rod 19R has the fore-and-aft length between its starting and terminal ends 19 a and 19 b, which is shorter than that of left link rod 19L, so that terminal end 19 b of right link rod 19R connected to the upper end portion of relay arm 81 is disposed forward from terminal end 19 b of left link rod 19L connected to the upper end portion of parking brake arm 78, as mentioned above.

Link rod 83 interposed between relay arm 81 and parking brake arm 78 is extended substantially in the fore-and-aft direction of vehicle 100 so as to have a front end serving as a starting end 83 a and a rear end serving as a terminal end 83 b. Referring to FIG. 2, link rod 83 is bent at starting and terminal ends 83 a and 83 b distally (i.e., rightward) toward transaxle casing 10, so that starting end 83 a of link rod 83 is fitted into connection hole 81 e in the lower end portion of relay arm 81, and terminal end 83 b of link rod 83 is fitted into connection hole 78 b in the lower end portion of parking brake arm 78. Starting end 83 a of link rod 83 has a pivotal axis P3 coinciding to a central axis of connection hole 81 e. In other words, starting end 83 a of link rod 83 and the lower end portion of relay arm 81 are connected to each other so that they are centered on pivotal axis P3 rotatably relative to each other. Terminal end 83 b of link rod 83 has a pivotal axis P4 coinciding to a central axis of connection hole 78 b. In other words, terminal end 83 b of link rod 83 and the lower end portion of parking brake arm 78 are connected to each other so that they are centered on pivotal axis P4 rotatably relative to each other.

The dimension of upper arm portion 81 a of relay arm 81 is determined so as to have a distance D1 from pivotal axis P1 to pivotal axis P2. The dimension of lower arm portion 81 b of relay arm 81 is determined so as to have a distance D2 from pivotal axis P1 to pivotal axis P3. The upper arm portion of relay arm 81 is shorter than the lower arm portion of relay arm 81 so that distance D1 is less than distance D2. This dimension setting of relay arm 81 having the difference between distances D1 and D2 corresponds to the difference between the length of link rod 19R from starting end 19 a to terminal end 19 b and the length of link rod 83 from starting end 83 a to terminal end 83 b. Due to small distance D1, the movement of link rod 19R and upper arm portion 81 a of relay arm 81 upwardly extended from trunnion shaft 45 is reduced so as to avoid their interference with pulley 92 rearward disposed therefrom, and on the other hand, due to large distance D2, the movement of link rod 83 and the rotation of parking brake arm 78 for applying parking brake 69 are enhanced efficiently relative to the reduced movement of link rod 19R.

In this way, each of transaxles 1R and 1L can be selectively designed to have parking brake arm 78 extended either upward or downward from brake operation shaft 79, and correspondingly, it can be selectively designed to have either a long link rod, such as foresaid left link rod 19L, directly connected at its terminal end to parking brake arm 78, if parking brake arm 78 is extended upward, or a short link rod, such as foresaid right link rod 19R, connected at its terminal end via relay arm 81 and link rod 83 to parking brake arm 78, if parking brake arm 78 is extended downward.

Description will be given of a mechanism for locating speed control arm 46 of representative right transaxle 1R with reference to FIGS. 1 and 12 to 15. Description of that of left transaxle 1L is omitted on the assumption that right and left transaxles 1R and 1L are symmetric as mentioned above. Trunnion shaft 45 and speed control arm 46, especially, their rotational directions, are referred to on the assumption that they appear in the right side view of right transaxle 1R as shown in FIGS. 12 to 15.

Referring to FIGS. 1, 12, 13 and 14, description will be given of the rotational range of speed control arm 46 corresponding to the operation range of control lever 60R for forwardly rotating corresponding axle 2R and drive wheel 3R. As mentioned above, the rear end of link rod 18 is fitted into connection hole 46 c in the upper end portion of speed control arm 46, thereby operatively connecting speed control arm 46 of right transaxle 1R to right control lever 60R via right link rod 18. Therefore, when right control lever 60R is rotated, right link rod 18 is pulled forward or pushed rearward, so that speed control arm 46 is rotated together with trunnion shafts 45 of movable swash plate 44 in right transaxle 1R. The rotation of speed control arm 46 and trunnion shafts 45 is centered on pivotal axis P1 that also serves as the pivotal axis for rotation of relay arm 81 relative to transaxle casing 10 of right transaxle 1R as mentioned above.

Referring to FIGS. 13 and 14, as control lever 60R is rotated forward from its neutral position for forwardly rotating right axle 2R, right link rod 18 moves rearward to rotate speed control arm 46 counterclockwise around pivotal axis P1 so as to increase fluid in quantity delivered from hydraulic pump 40 in the direction for driving hydraulic motor 50 for forward rotation of axle 2R. During this counterclockwise rotation of speed control arm 46, as understood from FIG. 14, pressure plate 46 b moves downward so as to push lower end portion El of neutral return spring 47 downward while upper end portion Eu of neutral return spring 47 is retained by eccentric pin 49 so as to be hindered from moving downward to follow lower end portion El, thereby generating the force of neutral return spring 47 to bias lower end portion El upward toward upper end portion Eu so as to bias speed control arm 46 toward its neutral position N where upper and lower end portions Eu and El of neutral return spring 47 pinch pressure plate 46 b therebetween (see FIGS. 12 and 13). Accurately, the force of neutral return spring 47 biases speed control arm 46 toward a later-discussed predetermined angle T1, however, until predetermined angle T1 is discussed, the force of neutral return spring 47 is temporarily defined as biasing speed control arm 46 toward neutral position N for the convenience of description.

Consequently, when the operator takes off right control lever 60R from the operator's hand after right control lever 60R reaches a target speed set position (for example, a maximum angle T2 in FIG. 14) in the forward rotational direction from the neutral position, speed control arm 46 automatically returns to a predetermined angle T1 by the biasing force of neutral return spring 47, and right control lever 60R automatically returns onto the neutral position side (very slow speed). This mechanism to automatically return speed control arm 46 and control lever 60R advantageously lightens the operator's loads in manipulation for reducing the traveling speed of right drive wheel 3R, and ensures safe and prompt speed reduction of drive wheel 3R in response to an operator's manipulation. The same mechanism that returns speed control arm 46 onto the neutral position side is also provided in left transaxle 1L, left link rod 18 and left control lever 60L.

However, conversely, the force of neutral return spring 47 biasing speed control arm 46 toward neutral position N means that the operator has to keep applying a force with the operator's hand to corresponding control lever 60R or 60L against the spring force of neutral return spring 47. In other words, the operator has to endure the resistance of control lever 60R or 60L against the operator's manipulation force, if the operator wants to keep the rotational speed of drive wheel 3R or 3L realized by locating control lever 60R or 60L at the corresponding speed set position.

During a normal on-road travel of vehicle 100, such a resistance of control lever 60R or 60L against the operator's manipulation force does not become a problem because the operator often rotates each of control levers 60R and 60L to change the rotational speed and direction of corresponding drive wheel 3R or 3L. In this traveling state of vehicle 100, the average speed of drive wheels 3R and 3L is rather high. On the contrary, a typical case where the problem occurs is that the lawn mower serving as vehicle 100 travels straight for a long time at a relatively low speed appropriate for mowing the lawn. During such a travel of vehicle 100, the operator has to hold right and left control levers 60R and 60L for a long time at respective determined speed positions against the resistances of control levers 60R and 60L.

Therefore, speed control arm 46 is configured so as to have a small rotational angle range where its rotation does not generate the spring force of neutral return spring 47 biasing speed control arm 46 toward neutral position N. In this regard, actually, speed control arm 46 located at its proper neutral position N accurately corresponding to the neutral position of movable swash plate 44 of hydraulic pump 40 is as shown in FIG. 12, where eccentric pin 49 abuts at the lower end thereof against lower end portion El of neutral return spring 47, and is separated at the upper end thereof from upper end portion Eu of neutral return spring 47 thereabove, while in halfways to upper and lower end portions Eu and El of neutral return spring 47 pinches pressure plate 46 b therebetween, i.e., to make upper and lower ends of pressure plate 46 b abut against in halfways to upper and lower end portions Eu and El of neutral return spring 47.

Referring to FIGS. 12 and 13, as speed control arm 46 is rotated counterclockwise from neutral position N, lower end portion El of neutral return spring 47 is pushed downward by pressure plate 46 b away from the lower end of eccentric pin 49, and upper end portion Eu of neutral return spring 47 tending to keep the gap between upper and lower end portions Eu and El of neutral return spring 47 to pinch pressure plate 46 b therebetween follows the downward movement of lower end portion El of neutral return spring 47 so as to approach the upper end of eccentric pin 49. When speed control arm 46 rotating counterclockwise from neutral position N reaches a predetermined angle T1, upper end portion Eu of neutral return spring 47 comes to abut against the upper end of eccentric pin 49.

In this way, during the rotation of speed control arm 46 between neutral position N and predetermined angle T1, the gap between upper and lower end portions Eu and El of neutral return spring 47 to pinch pressure plate 46 b therebetween is kept, in other words, upper and lower end portions Eu and El of neutral return spring 47 are kept to abut against the upper and lower ends of pressure plate 46 b, whereby neutral return spring 47 does not bias speed control arm 46 toward any position. Therefore, the rotational angle range of speed control arm 46 from neutral position N to predetermined angle T1 is defined as a dead zone d for neutral return spring 47 in generating its spring force to bias speed control arm 46 toward proper neutral position N as shown in FIG. 12.

In this regard, the technical feature for realizing the rotational angle range of speed control arm 46 as the dead zone d for neutral return spring 47 is that the dimension of pressure plate 46 b between its upper and lower ends is set greater than the diameter of eccentric pin 49 (between its upper and lower ends) so that upper and lower end portions Eu and El of neutral return spring 47 pinching pressure plate 46 b therebetween has the gap greater than the diameter of eccentric pin 49, thereby spacing at least one of upper and lower end portions Eu and El of neutral return spring 47 abutting against the upper and lower ends of pressure plate 46 b from eccentric pin 49. Therefore, the difference of the gap between upper and lower end portions Eu and El of neutral return spring 47 pinching pressure plate 46 b from the diameter of eccentric pin 49 equals the rotational angle range of speed control arm 46 between neutral position N and predetermined angle T1.

As far as control lever 60R is located in a low forward traveling speed setting range to locate speed control arm 46 at any one position in the rotational angle between neutral position N and predetermined angle T1, an operator can keep control lever 60R at a set desired low speed position to keep the constant low speed rotation of corresponding drive wheel 3R freely from the resistance of control lever 60R caused by the spring force of neutral return spring 47 of right transaxle 1R. Therefore, the low speed setting ranges of control levers 60R and 60L for setting respective speed control arms 46 in the rotational angle ranges between respective neutral positions N and respective predetermined angles T1 are available for traveling of vehicle 100 at a constant low speed as mentioned above, thereby being advantageous for lightening the operator from fatigue.

When speed control arm 46 is further rotated counterclockwise from predetermined angle T1 to maximum angle T2, the above-mentioned state of neutral return spring 47 generating its force biasing speed control arm 46 occurs, that is, upper end portion Eu of neutral return spring 47 is kept to abut against eccentric pin 49, and lower end portion El of neutral return spring 47 is moved downward by pressure plate 46 b so that the gap between upper and lower end portions Eu and El of neutral return spring 47 becomes greater than that to pinch pressure plate 46 b therebetween, thereby generating the spring force of neutral return spring 47 biasing speed control arm 46 in the clockwise rotational direction. Therefore, the middle and high speed setting ranges of control levers 60R and 60L for setting respective speed control arms 46 in the rotational angle ranges between respective predetermined angles T1 and respective maximum angles T2 are available for the on-road traveling of vehicle 100 at various speeds with a relatively high speed. If an operator unexpectedly releases control lever 60R or 60L having been located in the middle and high speed setting range from the operator's hand, corresponding speed control arm 46 automatically returns to predetermined angle T1 and decelerates so as to keep the safety in travel of vehicle 100.

Incidentally, the biasing force neutral return spring 47 for clockwise rotation of speed control arm 46 equals to the upward pressure of lower end portion El of neutral return spring 47 against the lower end of pressure plate 46 b. This upward pressure of lower end portion El of neutral return spring 47 is vanished when the upper end of pressure plate 46 b pushed upward by lower end portion El of neutral return spring 47 comes to abut against upper end portion Eu of neutral return spring 47. Pressure plate 46 b abuts against upper end portion Eu when speed control arm 46 rotating clockwise reaches predetermined angle T1. Therefore, as mentioned above, the spring force of neutral return spring 47 actually functions to bias speed control arm 46 toward predetermined angle T1 instead of neutral position N. To accurately stop each of drive wheels 3R and 3L, an operator has to consciously rotate corresponding control lever 60R or 60L to its neutral position by the operator's own manipulation force so as to set corresponding speed control arm 46 at neutral position N.

Referring to FIGS. 12 and 15, description will be given of the rotational range of speed control arm 46 corresponding to the operation range of control lever 60R for backwardly rotating corresponding axle 2R and drive wheel 3R.

As control lever 60R is rotated rearward from its neutral position for backwardly rotating right axle 2R, right link rod 18 moves forward to rotate speed control arm 46 clockwise around pivotal axis P1 from neutral position N to a maximum angle T3 as shown in FIG. 15, thereby increasing fluid in quantity delivered from hydraulic pump 40 in the direction for driving hydraulic motor 50 for backward rotation of axle 2R. Referring to FIG. 12, as mentioned above, when speed control arm 46 is located at neutral position N corresponding to the neutral position of movable swash plate 44, lower end portion El of neutral return spring 47 abuts against the lower end of eccentric pin 49. Therefore, as soon as the clockwise rotation of speed control arm 46 from neutral position N starts, pressure plate 46 b starts moving upward so as to separate its lower end from lower end portion El of neutral return spring 47 retained by eccentric pin 49 and so as to push upper end portion Eu of neutral return spring 47 upward, so that the gap between upper and lower end portions Eu and El of neutral return spring 47 becomes greater than that for pinching pressure plate 46 b, thereby causing the biasing force of neutral return spring 47 for counterclockwise rotation of speed control arm 46.

In this way, the clockwise rotation range of speed control arm 46 from neutral position N to maximum angle T3 in the direction for backward rotation of axle 2R does not include such a range corresponding to the dead zone d of neutral return spring 47 as mentioned above. Therefore, the biasing force of neutral return spring 47 applied to speed control arm 46 operated for backward rotation of axle 2R accurately biases speed control arm 46 toward neutral position N, so that, when control lever 60R having been rotated for backward rotation of axle 2R is released from the operator's manipulation force, control lever 60R automatically rotates forward until it reaches its neutral position corresponding to neutral position N of speed control arm 46. In this way, each of control levers 60R and 60L resists with the force of neutral return spring 47 against the operator's manipulation force if it is located at any position in its operation range for backward rotation of corresponding drive wheel 3R or 3L. Therefore, if control levers 60R and 60L having been located in these operation ranges are released from operator's hands, speed control arms 46 of respective transaxles 1R and 1L automatically return to respective neutral positions N by the forces of respective neutral return springs 47, so that vehicle 100 stops promptly.

It is further understood by those skilled in the art that the foregoing description is given to preferred embodiments of the disclosed apparatus and that various changes and modifications may be made in the invention without departing from the scope thereof defined by the following claims. 

What is claimed is:
 1. A transaxle comprising a continuously variable transmission including a speed control arm and a neutral return spring allowing a biasing force to act on the speed control arm toward a neutral position, the speed control arm configured to operate from the neutral position to a forward position or a backward position to perform a continuous speed variation, wherein the biasing force does not act on the speed control arm when the neutral return spring ranges from the neutral position to a predetermined speed position on a forward movement side, and the biasing force acts on the speed control arm when the neutral return spring ranges from the predetermined speed position to a maximum speed position on the forward movement side.
 2. The transaxle according to claim 1, wherein the biasing force acts on the neutral return spring in a whole range from the neutral position to a maximum speed position on a backward movement side.
 3. A vehicle comprising: the transaxle according to claim 2 in each drive wheel; and right and left control levers operated by a driver, the control lever being connected to each speed control arm.
 4. A transaxle comprising: a transaxle casing; an axle supported by the transaxle casing; a hydrostatic transmission disposed in the transaxle casing, wherein the hydrostatic transmission includes a hydraulic pump and a hydraulic motor fluidly connected to each other, wherein the hydraulic pump includes a movable swash plate having a trunnion shaft; a connecting member disposed outside of the transaxle casing, wherein the connecting member is pivotally supported on the trunnion shaft projected outward from the transaxle casing so that a rotary axis of the trunnion shaft serves as a rotary axis of the connecting member; a biasing member disposed so as to be rotatable about the axis of the trunnion shaft, wherein the biasing member includes a base portion formed with a shaft hole through which the trunnion shaft can be inserted, and a first arm portion and a second arm portion which are elastically deformable with respect to the base portion and project outward from the base portion in mutually different phase directions in a circumferential direction of the shaft hole; a pin positioned between the first arm portion and the second arm portion of the biasing member; wherein the connecting member is linked to a control lever via a link member, wherein the control lever is configured to be rotatable between a neutral position, a first position rotated in the first direction from the neutral position, and a second position rotated from the neutral position in the second direction, the connecting member is rotated in accordance with the rotation of the control lever so that a rotational position of the trunnion shaft can be changed via the connecting member, wherein the pin is configured such that when the biasing member rotates in the first direction, the second arm portion can be contacted, and when the biasing member rotates in the second direction, the first arm portion can be contacted, wherein the connecting member and the biasing member are disposed adjacent to each other in an axial direction of the trunnion shaft, wherein the connecting member has a pressing portion projecting from the connecting member toward the biasing member, and pinched between the first arm portion and the second arm portion, wherein when the connecting member rotates in the first direction, the pressing portion presses the first arm portion in the first direction and presses the second arm portion against the pin, and the biasing member biases the connecting member in the second direction, and when the connecting member rotates in the second direction, the pressing portion presses the second arm portion in the second direction and presses the first arm portion against the pin, and the biasing member biases the connecting member in the first direction, and wherein when the connecting member is in the neutral position, the first arm portion of the biasing member and the pin are separated from each other, and the second arm portion of the biasing member and the pin contact each other.
 5. The transaxle according to claim 4, wherein the first direction is a direction in which the axle is rotated forward, and the second direction is a direction in which the axle is rotated backward. 